diff --git a/packages/core/src/core/turn.test.ts b/packages/core/src/core/turn.test.ts
index be94945476..615cb47541 100644
--- a/packages/core/src/core/turn.test.ts
+++ b/packages/core/src/core/turn.test.ts
@@ -134,6 +134,44 @@ describe('Turn', () => {
       expect(turn.getDebugResponses().length).toBe(2);
     });
 
+    it('should not duplicate text in getResponseText when both chunks and consolidated response are present', async () => {
+      const mockResponseStream = (async function* () {
+        // Chunk 1
+        yield {
+          type: StreamEventType.CHUNK,
+          value: {
+            candidates: [{ content: { parts: [{ text: 'Hello' }] } }],
+          } as GenerateContentResponse,
+        };
+        // Chunk 2
+        yield {
+          type: StreamEventType.CHUNK,
+          value: {
+            candidates: [{ content: { parts: [{ text: ' world' }] } }],
+          } as GenerateContentResponse,
+        };
+        // Final consolidated response (as yielded by GeminiChat)
+        yield {
+          type: StreamEventType.CHUNK,
+          value: {
+            candidates: [{
+              content: { parts: [{ text: 'Hello world' }] },
+              finishReason: 'STOP'
+            }],
+          } as GenerateContentResponse,
+        };
+      })();
+      mockSendMessageStream.mockResolvedValue(mockResponseStream);
+
+      for await (const _ of turn.run({ model: 'm' }, [{ text: 'req' }], new AbortController().signal)) {
+        // consume stream
+      }
+
+      const text = turn.getResponseText();
+      // CURRENT BUGGY BEHAVIOR: "Hello  world Hello world"
+      expect(text).toBe('Hello world');
+    });
+
     it('should yield tool_call_request events for function calls', async () => {
       const mockResponseStream = (async function* () {
         yield {
diff --git a/packages/core/src/core/turn.ts b/packages/core/src/core/turn.ts
index cc5335981a..f4703ecc53 100644
--- a/packages/core/src/core/turn.ts
+++ b/packages/core/src/core/turn.ts
@@ -472,10 +472,21 @@ export class Turn {
    */
   getResponseText(): string {
     if (this.cachedResponseText === undefined) {
-      this.cachedResponseText = this.debugResponses
-        .map((response) => getResponseText(response))
-        .filter((text): text is string => text !== null)
-        .join(' ');
+      let result = '';
+      for (const response of this.debugResponses) {
+        const text = getResponseText(response);
+        if (text) {
+          // Heuristic to handle both delta and cumulative responses:
+          // If the new text starts with our current result, it's likely a cumulative
+          // update (or a redundant final consolidated response).
+          if (result && text.startsWith(result)) {
+            result = text;
+          } else {
+            result += text;
+          }
+        }
+      }
+      this.cachedResponseText = result;
     }
     return this.cachedResponseText;
   }